404 A. J. NICHOLSON 
determine their nature and they might equally well be proto- 
plasmic strands. In several cases, however, I have succeeded 
in tracing some of these fibres to the bundles of tracheal endings, 
so that some at least are tracheal in nature. 
It is possible that these vacuolated cells may be leucocytes 
as they agree in structure and size with Vanev’s (81) deserip- 
tion and illustrations of the leucocytes in the larva of Gastro - 
philus equi, but the fact that fibres enter them throws 
considerable doubt on this theory. 
The tracheal system in the ovaries is very highly developed. 
‘Tracheae from the fourth and fifth segments go to the ovaries 
and branches of “these penetrate the investing membrane. 
These tracheal trunks branch repeatedly in the space between 
the two ovarian sheaths. The final branches consist of exceed- 
ingly fine tubes, in which no spiral filament can be distinguished. 
‘These pass to the various parts of the ovary in bundles, the 
tubes being joined together by the tracheal cells which occur 
at intervals along the bundles. When such tracheal cells are 
cut transversely they appear to be very much vacuolated, 
owing to the numerous tubes passing through the cytoplasm. 
The individual tubes eventually become free from the bundles 
and end in the tissues of the ovary. 
A moderately large tracheal branch passes into the base of 
each follicular tube and gives rise to numerous bundies of 
tracheal endings. In the young ovary these have a very 
characteristic appearance, and are seen as a prominent coiled 
mass at the base of each follicular tube. This allows for 
expansion when the ovarian follicles inerease in size. The 
ultimate endings of these tubes are difficult to discover, but 
I have noted some entering cells of the ovarian follicles and 
isolated tracheal endings may be seen in almost any part of 
the follicular tubes. 
Inside the follicular tube is an egg-string consisting of an end 
chamber followed by two or three egg-follicles in various stages 
of development. ‘These follicles are joined together by cellular 
stalks consisting of a single row of cells (fig. 26). The last 
‘ stalk ’ or funicle runs from the posterior and most-developed 
